The present invention relates to integrated circuit structures and fabrication methods.
Ever since the mid-1980s, titanium nitride (TiN) has been a very common material for diffusion barrier layers in integrated circuit fabrication. However, with the increased demands on metallization and interconnect technology in the late 1990s, there is an increasing need for thin film structures with better diffusion-barrier and adhesion properties.
Ti--Al--N films have been proposed as one alternative. Ti--Al--N films are attractive for diffusion barriers in integrated circuit fabrication. The use of aluminum in the composition (instead of a pure TiN composition) produces an amorphous thin film, which is desirable for a diffusion barrier (since diffusion pathways along grain boundaries are eliminated). In such applications the Al fraction will form a thin but durable native oxide (which is primarily Al.sub.2 O.sub.3), so the material (like aluminum metal, but unlike TiN) self-passivates itself on exposure to air. See generally, e.g., Lee et al., "(Ti.sub.1-x Al.sub.x)N coatings by plasma-enhanced chemical vapor deposition," 12 J. VAC. Sci. TECHNOL. A 1602 (1994); Wahistrom et al., "Crystal growth and microstructure of polycrystalline Ti.sub.1-x Al.sub.x N alloy films deposited by ultra-high-vacuum dual-target magnetron sputtering," 235 THIN SOLID FILMS 62 (1993); Lee and Lee, "Compositionally gradient (Ti.sub.1-x Al.sub.x)N coatings made by plasma enhanced chemical vapor deposition," 13 J. VAC. SCI. TECHNOL. A 2030 (1995); Inoue et al., "Structure and composition of (Ti, Al)N films prepared by r.f. planar magnetron sputtering using a composite target," 271 THIN SOLID FILMS 15 (1995); all of which are hereby incorporated by reference.
Ti--Al--N films are also attractive for hard coatings for solid objects. Titanium nitride is often used for a friction-reducing or decorative layer, but is not stable against oxidation, and hence some protective overcoat is usually used. However, this increases the cost of such films, and may also reduce their durability.
Ti--Al--N films are normally made by one of two methods: reactive sputtering (PVD) using Ti--Al alloy targets in a nitrogen atmosphere; or by CVD using TiCl.sub.4 +NH.sub.3 +AlCl.sub.3. Reactive sputtering processes suffer from poor step coverage and limited range of Al/Ti ratio, while CVD processes require high substrate temperatures during deposition (which is a problem for multilayer metallization). CVD processes also risk a corrosive residue (e.g. Cl) and particle generation due to gas phase reactions.